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afsk1200.m
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afsk1200.m
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function [sig] = afsk1200(bits, fs, F_mark, F_space, bit_rate)
% The function will take a bitarray of bits and will output an AFSK1200 modulated signal of them, sampled at 44100Hz
% Dang Manh Truong (dangmanhtruong@gmail.com)
% References:
% [1] - https://inst.eecs.berkeley.edu/~ee123/sp17/lab/lab5/Lab5_Part_2-Audio_Frequency_Shift_Keying(AFSK).html
% Inputs:
% bits - bitarray of bits
% fs - sampling rate
% Outputs:
% sig - returns afsk1200 modulated signal
%
num_of_bits = numel(bits);
F_s = lcm(fs, bit_rate);
d_alpha_mark = 2* pi*F_mark/F_s;
d_alpha_space = 2* pi*F_space/F_s;
num_of_samples_per_bit = ceil(F_s / bit_rate);
alpha = 0;
idx = 1;
s_t = zeros(1, num_of_bits * num_of_samples_per_bit);
for ii = 1:num_of_bits
if bits(ii)==1
d_alpha = d_alpha_mark;
else
d_alpha = d_alpha_space;
end
for j = 1:num_of_samples_per_bit
alpha = alpha + d_alpha;
s_t(idx) = cos(alpha);
% s_t(idx) = exp(sqrt(-1) * alpha);
idx = idx + 1;
end
end
downsampling_rate = ceil(F_s / fs);
sig = s_t(1 : downsampling_rate : num_of_bits * num_of_samples_per_bit);
end